Most electrical household appliances have a large number of electrical loads distributed throughout the system, such as for example lamps, fans, valves, motors, etc., which are essential to the operation of the equipment and typically commanded by a control unit, which supplies or not voltage thereto as a function of the process requirements. The energization control of the loads is effected by semi-conducting electromechanical or triac AC switches, such as the electromagnetic relays, which are typically located in a power unit that receives the voltage from the power network and distributes it to the loads through adequate electrical cables. FIG. 1 shows a typical diagram of the electrical connections of a refrigerator 1 operatively connected to a power network 2 and comprises a control unit 3, a power unit 4, a fan 5, a defrost resistance 6, an internal lamp 7 and a compressor 8. As it can be noted, the existence of several loads in the system requires a large number of cables 9 distributed throughout the appliance, increasing the electromagnetic noise, the cost of the wirings and making difficult the mounting process, bearing in mind that the larger the number of loads and wirings the higher the complexity of the system.
In order to reduce the aforesaid problems related to the distribution of loads, the automobile industries have developed serial communication standards, aiming at eliminating the individual cables for each load of the system. Among said standards, CAN standard is the best known. For applications in which the system does not require high speed or high data flow, the so-called LIN standard has been developed. In said applications, the voltage is directly supplied to the load, which has a local power switch and the control unit 2 commands the selective energization of the load through serial communication. In both serial communication standards, the level of the signal used in the communication is different from the level of the voltage of the AC power network. Thus, for applications in household appliances, special circuits for conversion of signals should be used, as well as the installation of two additional conductors exclusively for the serial communication.
A serial communication standard known as X-10 specifies the serial communication directly through the power network by modulating a high frequency signal over the network, which signal is normally used for establishing communication between appliances in a home or to access the Internet, dispensing the installation of telephone or network cables. The great disadvantage of said standard is that it requires a usually complex and relatively expensive filtering circuit for separating the communication signal from the power network.
There is also the industrial communication standard known as AS-i, whose principle is similar to that of the already described X-10, in which supply voltage and communication travel through the same conductors, in different frequency spectra, in which case the supply voltage is in DC, usually of 24 Vdc. AS-i standard is widely used in industrial networks for communication with sensors and actuators.
It can be concluded from the basic description of some of the existing communication standards that all of them require complex dedicated electronic circuits to execute the tasks of separating and/or treating the signals, but which become infeasible in systems in which cost is a preponderant factor and which do not require high speed or transmitted data high flow.